The invention concerns a device and a method for the closed-loop control of an exhaust gas turbocharger with variable turbine geometry.
Exhaust gas turbochargers are used to boost the performance of internal combustion engines. The exhaust gas turbocharger can be better adapted to an operating point of the internal combustion engine by means of a variable turbine geometry, e.g., adjustable guide vanes. To guarantee constant setting accuracy, the exhaust gas turbocharger is operated in a closed-loop control system. In a closed-loop control system of this type, the exhaust gas turbocharger with variable turbine geometry is the controlled system. The actual charge air pressure is detected as the controlled variable and compared with the reference input, i.e., the set charge air pressure. A charge air pressure controller uses this control deviation to determine the correcting variable for acting on the controlled system. The correcting variable typically corresponds to the flow-through cross-sectional area of the turbine.
DE 697 12 056 T2 describes a control system for an exhaust gas turbocharger with variable turbine geometry. The control system comprises four closed-loop control systems arranged in parallel, namely, a first closed-loop control system for automatically controlling the exhaust gas pressure, a second closed-loop control system for automatically controlling the charge air pressure, a third closed-loop control system for automatically controlling the pressure difference between the exhaust gas pressure and the charge air pressure, and a fourth closed-loop control system for automatically controlling the turbine speed of the exhaust gas turbocharger. The four closed-loop control systems act on the same controlled system. During the operation of the internal combustion engine, only one of the closed-loop control systems is dominant, i.e., active, at any given time. The switching from one closed-loop control system to another closed-loop control system is event-controlled, e.g., as a function of a turbine speed limit or a braking mode. This control system conversion is complicated and allows automatic control of only a single controlled variable. The changes in dominance from one controller to another controller are likewise critical.